.\" $NetBSD: shquote.3,v 1.9 2008/09/07 08:55:46 apb Exp $
.\"
.\" Copyright (c) 2001 Christopher G. Demetriou
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.\" <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
.\"
.Dd September 7, 2008
.Dt SHQUOTE 3
.Os
.Sh NAME
.Nm shquote ,
.Nm shquotev
.Nd quote argument strings for use with the shell
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft size_t
.Fn shquote "const char *arg" "char *buf" "size_t bufsize"
.Ft size_t
.Fn shquotev "int argc" "char * const *argv" "char *buf" "size_t bufsize"
.Sh DESCRIPTION
The
.Fn shquote
and
.Fn shquotev
functions copy strings and transform the copies by adding shell
escape and quoting characters.
They are used to encapsulate
arguments to be included in command strings passed to the
.Fn system
and
.Fn popen
functions, so that the arguments will have the correct values
after being evaluated by the shell.
.Pp
The exact method of quoting and escaping may vary, and is intended
to match the conventions of the shell used by
.Fn system
and
.Fn popen .
It may not match the conventions used by other shells.
In this implementation, the following
transformation is applied to each input string:
.Bl -bullet -width indent
.It
it is surrounded by single quotes
.Pq ' ,
.It
any single quotes in the input are escaped by replacing them with
the four-character sequence:
.Li '\e'' ,
and
.It
extraneous pairs of single quotes (caused by multiple adjacent single
quotes in the input string, or by single quotes at the beginning or
end of the input string) are elided.
.El
.Pp
The
.Fn shquote
function transforms the string specified by its
.Fa arg
argument, and places the result into the memory pointed to by
.Fa buf .
.Pp
The
.Fn shquotev
function transforms each of the
.Fa argc
strings specified by the array
.Fa argv
independently.
The transformed strings are placed in the memory pointed to by
.Fa buf ,
separated by spaces.
It does not modify the pointer array specified by
.Fa argv
or the strings pointed to by the pointers in the array.
.Pp
Both functions write up to
.Fa bufsize
- 1 characters of output into the buffer pointed to by
.Fa buf ,
then add a
.Li NUL
character to terminate the output string.
If
.Fa bufsize
is given as zero, the
.Fa buf
parameter is ignored and no output is written.
.Sh RETURN VALUES
The
.Fn shquote
and
.Fn shquotev
functions return the number of characters necessary to hold the
result from operating on their input strings,
not including the terminating
.Li NUL .
That is, they return the length of the string that would have
been written to the output buffer, if it were large enough.
If an error occurs during processing, the value ((size_t)\-1)
is returned and
.Va errno
is set appropriately.
.Sh EXAMPLES
The following code fragment demonstrates how you might use
.Fn shquotev
to construct a command string to be used with
.Fn system .
The command uses an environment variable (which will be expanded by
the shell) to determine the actual program to run.
Note that the environment variable may be expanded by
the shell into multiple words.
The first word of the expansion will be used by the shell
as the name of the program to run,
and the rest will be passed as arguments to the program.
.Bd -literal -offset indent
char **argv, c, *cmd;
size_t cmdlen, len, qlen;
int argc;

\&...

/*
 * Size buffer to hold the command string, and allocate it.
 * Buffer of length one given to snprintf() for portability.
 */
cmdlen = snprintf(\*[Am]c, 1, "${PROG-%s} ", PROG_DEFAULT);
qlen = shquotev(argc, argv, NULL, 0);
if (qlen == (size_t)-1) {
	\&...
}
cmdlen += qlen + 1;
cmd = malloc(cmdlen);
if (cmd == NULL) {
	\&...
}

/* Create the command string. */
len = snprintf(cmd, cmdlen, "${PROG-%s} ", PROG_DEFAULT);
qlen = shquotev(argc, argv, cmd + len, cmdlen - len);
if (qlen == (size_t)-1) {
	/* Should not ever happen. */
	\&...
}
len += qlen;

/* "cmd" can now be passed to system(). */
.Ed
.Pp
The following example shows how you would implement the same
functionality using the
.Fn shquote
function directly.
.Bd -literal -offset indent
char **argv, c, *cmd;
size_t cmdlen, len, qlen;
int argc, i;

\&...

/*
 * Size buffer to hold the command string, and allocate it.
 * Buffer of length one given to snprintf() for portability.
 */
cmdlen = snprintf(\*[Am]c, 1, "${PROG-%s} ", PROG_DEFAULT);
for (i = 0; i \*[Lt] argc; i++) {
	qlen = shquote(argv[i], NULL, 0);
	if (qlen == (size_t)-1) {
		\&...
	}
	cmdlen += qlen + 1;
}
cmd = malloc(cmdlen);
if (cmd == NULL) {
	\&...
}

/* Start the command string with the env var reference. */
len = snprintf(cmd, cmdlen, "${PROG-%s} ", PROG_DEFAULT);

/* Quote all of the arguments when copying them. */
for (i = 0; i \*[Lt] argc; i++) {
	qlen = shquote(argv[i], cmd + len, cmdlen - len);
	if (qlen == (size_t)-1) {
		/* Should not ever happen. */
		\&...
	}
	len += qlen;
	cmd[len++] = ' ';
}
cmd[--len] = '\e0';

/* "cmd" can now be passed to system(). */
.Ed
.Sh SEE ALSO
.Xr sh 1 ,
.Xr popen 3 ,
.Xr system 3
.Sh BUGS
This implementation does not currently handle strings containing multibyte
characters properly.
To address this issue,
.Pa /bin/sh
.Po
the shell used by
.Fn system
and
.Fn popen
.Pc
must first be fixed to handle multibyte characters.
When that has been done,
these functions can have multibyte character support enabled.
